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At least 73 records · Page 4

Machine-learned quantum molecular dynamics calculations of warm dense equation of state and ionic transport coefficients of deuterated water

White dwarf models require accurate equations of state and ionic transport coefficients in the warm dense matter regime, where kinetic theory models and tabulated equations of state are often inaccurate. In this work, spectral-partitioned density functional theory and machine-learned interatomic potentials are combined to perform large-scale, first-principles quantum molecular dynamics simulations of deuterated water (D 2 O) near the principal Hugoniot. This approach retains Kohn-Sham accuracy while achieving orders-of-magnitude speedup, yielding converged equation of state and transport properties over a broad pressure and temperature range. The results reveal the thermodynamic conditions under which ionic transport models for interdiffusivity and shear viscosity converge and identify those in closest agreement with density functional theory benchmarks at temperatures in the warm dense matter regime. The present framework extends first-principles transport calculations to higher temperatures than previously achieved, and provides an efficient, scalable, and general approach for studying transport properties in complex multicomponent mixtures.

79 ASTRONOMY AND ASTROPHYSICS↗

Test of a new field-theoretical crossover equation-of-state

A new field-theoretical crossover equation-of-state model provides a bridge between the asymptotic behavior close to a liquid-gas critical point and the expected mean field behavior farther away.

equation-of-state critical phenomena liquid-gas cr↗

Astrophysical Applications of Quantum Corrections to the Equation of State of a Plasma

The quantum electrodynamic correction to the equation of state of a plasma at finite temperature is applied to the areas of solar physics and cosmology. A previously neglected, purely quantum term in the correction is found to change the equation of state in the solar core by -0.37%, which is roughly estimated to decrease the calculated high energy neutrino flux by about 2.2%. We also show that a previous calculation of the effect of this correction on big bang nucleosynthesis is incomplete, and we estimate the correction to the primordial helium abundance Y to be Delta A= 1.4 x 10(exp -4). A physical explanation for the correction is found in terms of corrections to the dispersion relation of the electron, positron, and photon.

Heckler, Andrew F.↗

Scaled equation of state parameters for gases in the critical region

In the light of recent theoretical developments, the paper presents an accurate characterization of anomalous thermodynamic behavior of xenon, helium 4, helium 3, carbon dioxide, steam and oxygen in the critical region. This behavior is associated with long range fluctuations in the system and the physical properties depend primarily on a single variable, namely, the correlation length. A description of the thermodynamic behavior of fluids in terms of scaling laws is formulated, and the two successfully used scaled equations of state (NBS equation and Linear Model parametric equation) are compared. Methods for fitting both equations to experimental equation of state data are developed and formulated, and the optimum fit for each of the two scaled equations of the above gases are presented and the results are compared. By extending the experimental data for the above one-component fluids to partially miscible binary liquids, superfluid liquid helium, ferromagnets and solids exhibiting order-disorder transitions, the principle of universality is concluded. Finally by using this principle, the critical regions for nine additional fluids are described.

Sengers, J. M. H. L.↗

Platform for 100 s Mbar equation of state measurements on the National Ignition Facility

Equation of state (EOS) measurements in the 100 s Mbar range are needed to underwrite models employed in the simulation of high energy density plasmas. To this end, a platform has been developed for fielding on the National Ignition Facility, capable of producing high-quality impedance match EOS data, wherein a planar, high-pressure, steady shock is driven into a sample package, and sample and reference standard shock velocities are measured. This platform, dubbed planar high pressure, or PHP, was fielded with an initial proof-of-concept shot in January 2023. The first PHP shot, aiming to study gold, demonstrated a pressure close to 400 Mbar, two orders of magnitude higher than previously reported gold EOS data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Effects from equation of state and rheology in dissipative heating in compressible mantle convection

The effects of compressibility on mantle convection are considered, incorporating the effects of equations of state and rheology in the dissipative heating term of the energy equation. The ways in which compression may raise the interior mantle temperature are explicitly demonstrated, and it is shown how this effect can be used to constrain some of the intrinsic parameters associated with the equation of state in the mantle. It is concluded that the coupling between variable viscosity and equation of state in dissipative heating is potentially an important mechanism in mantle convection. These findings emphasize that rheology, equation of state, and radiogenic heating are all linked to each other by nonlinear thermomechanical couplings.

Yuen, David A.↗

Ion equation of state in quasi-parallel shocks - A simulation result

Ion equation of state in the quasi-parallel collisionless shock is deduced from simulation results. The simulations were performed for theta(bn) = 10 deg, beta = 0.5 and M sub A in the range from 1.2 to 8, where M sub A is the Alfven Mach number, beta is the upstream ratio of plasma pressure to magnetic pressure, and theta(bn) is the angle between the shock normal and the upstream magnetic field. The equation of state can be approximated by a power law with different exponents in the upstream and downstream sides of the shock transition region. The exponent in the upstream side of the transition region is much greater than the adiabatic value of 5/3 and increases with M sub A. The exponent in the downstream side of the transition region is slightly less than 5/3. The results show that ion heating in the quasi-parallel shock is highly nonadiabatic with a large increase in entropy and in temperature ratio in the upstream side of the transition region, while the heating is highly isentropic with a large increase in temperature difference across the principal density jump in the downstream side of the transition region.

Mandt, M. E.↗

Equation of state of boron carbide B 4 ⁢C

We present the results of recent experiments conducted on the Sandia Z machine and a new tabular equation of state for B 4 ⁢C. The equation of state was calibrated to a combination of density functional calculations reported here and fits to preexisting data. It was constructed partly to recover the effects of a shock-driven, polymorphic phase transition of unknown character beginning at particle velocities of just under 3 km/s (shock pressures of 95 GPa). Some of the Z experiments included sound speeds determined by the overtaking rarefaction method, from which we calculate the Grüneisen parameter and compare with previous experiments conducted at the OMEGA laser [Fratanduono et al ., Phys. Rev. B 94 , 184107 (2016)], our own first principles calculations, and another recent tabular equation of state [Zhang et al ., Phys. Rev. E 102 , 053203 (2020)]. We also compare our results with previous static compression, thermophysical, and melt studies, finding mixed consistency. We predict the onset and completion of shock melting at 225 and 265 GPa, respectively, and predict a melt curve that is largely flat to pressures of several hundred GPa.

36 MATERIALS SCIENCE↗

Neutron stars and the dense matter equation of state

The past two decades have witnessed tremendous progress in understanding the properties of neutron stars, their maximum mass and radii, and the properties of the dense matter in their cores, made possible by electromagnetic observations of neutron stars and the detection of gravitational waves from their mergers. These observations have provided novel constraints on neutron-star structure that are intimately related to the properties of dense neutron-rich matter described by the nuclear equation of state. Nevertheless, constraining the equation of state over the wide range of densities probed by astrophysical observations is still challenging, as the physics involved is broad and the system spans many orders of magnitude in density. Here, theoretical approaches to calculate and model the neutron-star equation of state in various regimes of densities are reviewed, and the related consequent properties of neutron stars are discussed. How the equation of state at low densities can be calculated from nuclear interactions that are constrained and benchmarked by nuclear experiments is described. Neutron-star observations, with a particular emphasis on information provided by gravitational-wave signals and electromagnetic observations, are reviewed. Finally, future challenges and opportunities in the field are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Equation of state of matter at supernuclear densities.

The qualitative features of the equation of state of matter at supernuclear densities are deduced through a careful examination of the nature of particle interactions at short distances and by the introduction of an 'effective baryon mass spectrum.' It is found that the equation of state begins to take on a particularly simple form (the 'asymptotic form') at a relatively low matter density of 100,000 teragrams per cu cm.

Leung, Y. C.↗

The shock wave equation of state of brucite Mg(OH)2

New shock equation of state (EOS) data on magnesium hydroxide between 12 and 60 GPa is presented. It is found that the brucite EOS data between 12 and 97 GPa can be fit with a single linear U(s) - u(p) relationship: U(s) = 4.76(0.11) + 1.35(0.05)u(p). The third order Birch-Murnaghan equation parameters are K(os) = 51 + or - 4 GPa and K(os)prime = 5.0 + or - 0.4. The first partial release states measured for brucite Mg(OH)2 are reported. Calculated phase boundaries using the EOS data are found to be consistent with the experimental data and indicate that brucite is unlikely to be stable under lower mantle conditions. At high pressure, bulk sound velocities calculated for MgO and Mg(OH)2 are very similar, indicating that the presence of hydrous assemblages in the lower mantle may not produce anomalous bulk seismic velocities. A comparison of densities in brucite and other high-pressure phases under mantle conditions shows that the water content of the lower mantle is between 0 and 3 wt pct.

Duffy, Thomas S.↗

Determining the nuclear equation of state from neutron-star masses and radii

A method is developed for determining the nuclear equation of state directly from a knowledge of the masses and radii of neutron stars. This analysis assumes only that equilibrium neutron-star matter has the stress-energy tensor of an isotropic fluid with a barotropic equation of state, and that general relativity describes a neutron star's internal gravitational field. We present numerical examples which illustrate how well this method will determine the equation of state when the appropriate observational data become available.

Lindblom, Lee↗

Universal features of the equation of state of solids

A study of the energetics of solids leads to the conclusion that the equation of state for all classes of solids in compression can be expressed in terms of a universal function. The form of this universal function is determined by scaling experimental compression data for measured isotherms of a wide variety of solids. The equation of state is thus known (in the absence of phase transitions), if zero-pressure volume and isothermal compression and its pressure derivative are known. The discovery described in this paper has two immediate consequences: first, despite the well known differences in the microscopic energetics of the various classes of solids, there is a single equation of state for all classes in compression; and second, a new method is provided for analyzing measured isotherms and extrapolating high-pressure data from low-pressure (e.g. acoustic) data.

Vinet, Pascal↗

Equation-of-state spinning fluids in the Einstein-Cartan theory

The relativistic fluid equations may be completed in two physically distinct methods. One method assumes the mass, rho, (or particle number) is conserved, while the other method assumes an equation of state of the form P = P(rho). A variational principle for the mass conservation method both with and without an intrinsic spin for the fluid was constructed earlier (Ray and Smalley, 1982 and 1983). A variational principle for the fluid described by an equation of state both with and without spin is formulated. In all cases the variational principle is set in the Einstein-Cartan metric-torsion U4 geometry. The results for general relativity follow as a special case.

Ray, John R.↗

Equation of state and phase diagram of dense hydrogen

The equation of state of hydrogen was calculated for specific volumes ranging from 0.01 to 0.0001 cm3/mole and for temperatures ranging from 200 to 1 million K. Three phases are considered: the molecular solid, the metallic solid and the fluid. Chemical equilibrium between molecules, atoms, ions and electrons is considered in calculating the properties of the fluid phase. Transitions between the three phases will be discussed. The triple point, where the three phases coexist, is calculated to occur at 2.3 Mbar and 1679 K. At higher temperatures and pressures, the molecular solid is unstable.

Kerley, G. I.↗

The effect of the Mihalas, Hummer, and Daeppen equation of state and the molecular opacity on the standard solar model

Improvements to the Yale Rotating Stellar Evolution Code (YREC) by incorporating the Mihalas-Hummer-Daeppen equation of state, an improved opacity interpolation routine, and the effects of molecular opacities, calculated at Los Alamos, have been made. the effect of each of the improvements on the standard solar model has been tested independently by computing the corresponding solar nonradial oscillation frequencies. According to these tests, the Mihalas-Hummer-Daeppen equation of state has very little effect on the model's low l p-mode oscillation spectrum compared to the model using the existing analytical equation of state implemented in YREC. On the other hand, the molecular opacity does improve the model's oscillation spectrum. The effect of molecular opacity on the computed solar oscillation frequencies is much larger than that of the Mihalas-Hummer-Daeppen equation of state. together, the two improvements to the physics reduce the discrepancy with observations by 10 microHz for the low l modes.

Kim, Y.-C.↗